Henge: "Method of arranging big rocks to maximise future generation rip-off potential. Stones cost nothing originally, there being no recognised currency or managed exchange rate, yet over several millennia a henge can reach such a value that it's owners (human race) will be required to pay huge sums of money just to view, not touch, a henge. The henge as a business plan has an enviable return rate of infinity (nothing in, lots out), it's only downside being the unusually long payback period."

Still miffed about the entry fee then mate

Got a wall in my graden you can touch, only a fiver to get in too!